Earthquakes Are East Coast's Biggest Tsunami Threat

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The U.S. East Coast's biggest tsunami threat lurks just offshore,
according to research presented today (April 19) at the
Seismological Society of America's annual meeting in Salt Lake
City.

Recent earthquake swarms off the Massachusetts coast highlight
the threat of tsunamis from nearby earthquakes, rather than
faraway islands, said John Ebel, a seismologist at Boston
College.

The geologic setting of the quakes off the Northeast appears
similar to that of a magnitude-7.3 earthquake that struck in the
Grand Banks off Newfoundland in 1929, Ebel said. The resulting
32-foot (10 meters) tsunami swamped southern Newfoundland and
triggered
underwater landslides that severed transatlantic telephone
cables.

"We have to consider the possibility that there could be a Grand
Banks-style earthquake in these areas and a tsunami that could
affect the Northeast coast," Ebel told OurAmazingPlanet.

Ebel said that when he discusses tsunami hazards with emergency
planners, many think the East Coast's biggest risk is from
eruptions or underwater landslides at volcanic islands on the
other side of the Atlantic Ocean, such as the
Canary Islands.

The 1929 Newfoundland quake was felt from Canada to New York,
across hundreds of miles. If a similar temblor were to hit under
the seafloor today, residents would have 10 to 15 minutes of
warning before a tsunami would clobber the coast, Ebel said.

Ebel has also found small earthquakes, in the magnitude-2 and
magntiude-3 range, offshore as far south as southern New Jersey,
he will report today at the meeting. The offshore rumbles
indicate the areas most likely to have large, damaging
earthquakes in the future, he said.

That the offshore
earthquakes mostly stop south of New Jersey is a surprise,
Ebel said. Onshore, a powerful magnitude-7.3 earthquake hit
Charleston, S.C., in 1886.

Although it's only a guess, Ebel thinks the increased seismicity
from New Jersey to Nova Scotia could be related to changes that
have occurred since the last Ice Age. For instance, the crust is
flexing, now that its heavy load of ice and glacial lakes have
disappeared.

"As soon as you get away from the glaciers, you don't have
seismicity, but it could be a coincidence," Ebel said.

Researchers are also searching for signs of past tsunamis on the
East Coast. A possible 2,400-year-old tsunami deposit has been
found in New Hampshire, Ebel said.